Method of determining the amount of travel of a rotating component

ABSTRACT

A method of determining the amount of travel of a rotating component that includes a rotor shaft includes providing a self-contained magnetically-powered encoder. The encoder includes an encoder rotor that extends outward from a sealed housing such that a clearance gap is defined between the rotor and housing. The method also includes rotatably coupling the encoder to the rotor shaft. The method further includes measuring a first position of the encoder rotor and determining a first rotational position measurement of the rotor shaft based on the encoder rotor. The method also includes rotating the rotor shaft to a second rotational position and determining a direction of rotation and a second rotational position measurement of the rotor shaft using the encoder. The method further includes determining a total rotational distance traveled by the rotor shaft between the first rotational position and the second rotational position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/428,966, filed Jul. 6, 2006 now U.S. Pat. No. 7,728,583, which ishereby incorporated by reference and is assigned to the assignee of thepresent invention.

BACKGROUND OF THE INVENTION

This invention relates generally to rotary machines and moreparticularly, to methods and apparatus for monitoring rotary machines.

Some known wells, such as oil wells, are formed by drilling a boreholewithin a natural formation below the surface of the Earth. Suchformations may be found below land-based surfaces and/or submergedsurfaces. Some known drilling methods use powered rotating equipment toinduce torque to a drill pipe that subsequently rotates a drill bit. Therotating drill bit bores into the formation and generates cuttings ofthe formation to form a drilling well while appropriate fluids thatfacilitate transporting the cuttings to the surface are circulatedwithin the well. The drill pipe is lowered and raised within thedrilling well by a support cable extending from a drawworks drum. Whenrotating, the drawworks drum extends and retracts the cable to cause thedrill pipe to be lowered and raised, respectively. A pre-determined rateand amount of drill bit movement within the drilling well is influencedby a number of variables that include, but are not limited to a hardnessof the formations being drilled and/or a need to withdraw the drill pipefrom the well to replace the drill bit. Facilitation of the drillingactivities is at least partially attained by determining a depth of thedrill bit within the well. The drill bit depth is typically attained bymonitoring the length of drill pipe inserted into the drilling well, aswell as the rate and direction of movement of the drill pipe.

To facilitate determining such drill bit depth, some known drillingassemblies include drill bit measurement devices including encoders thatmeasure the rotation of the drawworks drum. The encoders transmit datato a monitoring system that correlates rotation of the drawworks drum toa drill pipe depth. However, because some known encoders require anexternal power source to supply a power level above 0.25 watts andvoltages above 24 volts DC, such encoders may not be suitable for use inareas wherein an ignitable environment may exist.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method of determining the amount of travel of arotating component that includes a rotor shaft is provided. The methodincludes providing a self-contained magnetically-powered encoder thatincludes at least one encoder rotor that extends outward from a sealedhousing such that a clearance gap is defined between the rotor andhousing. The method also includes rotatably coupling the encoder to therotor shaft. The method further includes measuring a first position ofthe encoder rotor and determining a first linear position measurement ofthe rotor shaft based on the encoder rotor. The method also includesrotating the rotor shaft to a second position and determining adirection of rotation and a second linear position measurement of therotor shaft using the encoder.

In another aspect, an encoder for use with a rotary machine including atleast one moveable member is provided. The encoder includes at least onesensor configured to activate via magnetic flux. The encoder isconfigured to dissipate electrical signals with a power amplitude thatis less than approximately one microwatt.

In a further aspect, a measurement system for a drilling assemblyincluding at least one rotatable member is provided. The system includesan encoder including at least one sensor configured to activate viamagnetic flux. The encoder is configured to dissipate electrical signalswith a power amplitude that is less than approximately one-third of onemicrowatt. The system also includes at least one processor coupled inelectronic data communication with the encoder via at least one inputchannel. The at least one processor is configured to receive and processat least one encoder output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary well drilling rig;

FIG. 2 is a schematic view of an exemplary encoder that may be used withthe drilling rig shown in FIG. 1;

FIG. 3 is a side view of the encoder shown in FIG. 2;

FIG. 4 is an electrical schematic of an exemplary drill pipe positionmeasurement system that may be used with the drilling rig shown in FIG.1; and

FIG. 5 is an exemplary graphical representation of waveforms that may beproduced using the encoder shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of an exemplary well drilling rig 100. In theexemplary embodiment, rig 100 is a rotary well top drive drilling rig100. Alternatively, rig 100 may be any drilling apparatus in which theinvention described herein may be embedded. Rig 100 includes a platform102 onto which a support structure, or derrick 104, is coupled. A crownblock 106 is suspended from derrick 104. Rig 100 also includes adrawworks 108 that includes a drum 110 that is powered by a power source(not shown in FIG. 1) that may include, but is not limited to, anelectric drive motor. Alternatively, the power source may be any devicethat enables rig 100 to function as described herein. Specifically, inthe exemplary embodiment, the power source is coupled to a drawworksdrive shaft 112 that is rotatably coupled to drum 110.

A cable 114 is wound around drum 110 and extends from drum 110 to crownblock 106. Cable 114 is coupled to crown block 106, in a manner similarto a pulley system that facilitates a pre-determined mechanicaladvantage thereby facilitating support of a traveling block 116 by crownblock 106. Traveling block 116 supports a rotary drive apparatus 118 viaa suspension member 120. In the exemplary embodiment, member 120 mayinclude, but is not limited to being a hook and swivel assembly.Alternatively, member 120 is any device that enables rig 100 to functionas described herein. Apparatus 118 is powered by a power source (notshown in FIG. 1). For example, in the exemplary embodiment, apparatus118 is an electric motor-driven top drive 118.

Top drive 118 is rotatably coupled to a kelly 122. In the exemplaryembodiment, kelly 122 is, but is not limited to being, a square orhexagonal member. Alternatively, kelly 122 may have any configurationthat enables rig 100 to function as described herein. Kelly 122 isrotatably coupled to a drill pipe 124 and is configured to transfertorque from top drive 118 to drill pipe 124. A guide member 123facilitates radial support of kelly 122. Drill pipe 124 is rotatablycoupled to at least one drill bit 126 used to form a borehole or well128. Alternative embodiments of drilling rig 100 may include a swiveljoint in the place of top drive 118 and a power-driven square orhexagonal bushing in the place of guide member 123.

Rig 100 also includes a drill pipe position measurement system 150 thatincludes at least one encoder 152 that is rotatably coupled to driveshaft 112 and that is electrically coupled to an interface device 154via an encoder cable 156. In the exemplary embodiment, encoder cable 156is an insulated and shielded copper cable and device 154 is a Safe AreaInterface (SAI) device 154 that is commercially available from GeneralElectric Energy, Twinsburg, Ohio. Interface device 154 is positioned adistance from platform 102 within an environment that facilitateshousing for a plurality of electronic apparatus (not shown in FIG. 1)included within device 154. Positioning device 154 in a remote locationa predetermined distance from platform 102 also facilitates mitigatingthe potential for introducing inadvertent electrical arcing in thevicinity of well 128. Interface device 154 is electrically coupled to adata processing assembly 158 that is coupled to an operator interfaceterminal (OIT) 160 via a plurality of electronic cables 162. In theexemplary embodiment, electronic cables 162 are serial and/or universalserial bus (USB) cables. Also, in the exemplary embodiment, assembly 158and OIT 160 are coupled as a portable laptop computer. Alternatively,assembly 158 and OTT 160 are separate units.

Device 154 and data processing assembly 158 both include at least oneprocessor and a memory (neither shown in FIG. 1). As used herein, theterm computer is not limited to just those integrated circuits referredto in the art as a computer, but broadly refers to a processor, amicrocontroller, a microcomputer, a programmable logic controller (PLC),an application specific integrated circuit, and other programmablecircuits, and these terms are used interchangeably herein. In theexemplary embodiment, memory may include, but is not limited to, acomputer-readable medium, such as a random access memory (RAM).Alternatively, a floppy disk, a compact disc—read only memory (CD-ROM),a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) mayalso be used. Also, in the exemplary embodiment, additional inputchannels may be coupled to computer peripherals associated with OIT 160,such as, but not limited to, a mouse and/or a keyboard. Alternatively,other computer peripherals may also be used including, for example, ascanner. Furthermore, in the exemplary embodiment, additional outputchannels may be coupled to additional data displays, printers, plottersand/or operational control mechanisms.

Processors for interface device 154 and assembly 158 processinformation, including signals received from encoder 152 and device 154.RAM devices store and transfer information and instructions to beexecuted by the processor. RAM devices can also be used to store andprovide temporary variables, static (i.e., non-changing) information andinstructions, and/or other intermediate information to the processorsduring execution of instructions by the processors. Instructions thatmay be executed include, but are not limited to including, residentconversion, calibration and/or comparator algorithms. The execution ofsequences of instructions is not limited to any specific combination ofhardware circuitry or software instructions.

During operation of rig 100, drill pipe 124 and drill bit 126 aresuspended within well 128. Top drive 118 transfers torque and rotationalmovement to kelly 122 which transfers the torque and rotational movementto drill pipe 124 and drill bit 126. A downward force is also inducedonto drill bit 126 by the weight of components positioned above bit 126and this force facilitates penetration of the formation being drilled.Traveling block 116 is positioned via multiple loops of cable 114coupled between traveling block 116 and crown block 106. To modulate thedownward force induced to drill bit 126, drawworks drum 110 is rotatedto withdraw or extend a portion of cable 114. The withdrawal andextension of cable 114 causes traveling block 116 to be raised orlowered such that the downward force induced on drill bit 126 issubsequently decreased or increased. Subsurface formation cuttings (notshown in FIG. 1) loosened by drill bit 126 are transported to thesurface by circulation of fluids through drill bit 126 and are removedvia a material removal sub-system (not shown in FIG. 1). As material isremoved from well 128 and the depth of well 128 is increased, drill pipe124 is lowered into well 128 to permit drill bit 126 to bore deeper.Specifically as drill pipe 124 is lowered, drum 110 is rotated to extenda portion of cable 114. The length of cable 114 extended may becorrelated to a depth of drill pipe 124 and to a number of rotations ofdrum 110. Occasionally, as a depth of well 128 increases, additionalsections of drill pipe 124 may need to be added to rig 100.

FIG. 2 is a schematic view of exemplary encoder 152 that may be usedwith well drilling rig 100 (shown in FIG. 1). FIG. 3 is a side view ofencoder 152. Encoder 152 includes a housing 164 that defines an encoderinternal cavity 166 therein. Housing 164 seals cavity 166 from theexternal environment of encoder 152 and facilitates protection from dustand water.

Encoder 152 also includes a rotor 168 that is rotatably coupled todrawworks drive shaft 112 (shown in FIG. 1). Rotor 168 extends throughhousing 164 via a seal assembly (not shown) that facilitates mitigatinginteraction between the external environment and cavity 166. Rotor 168rotates about an axis of rotation 169. Housing 164 and rotor 168 areoriginated such that a radially outermost surface 170 of rotor 168 and aradially innermost surface 172 of housing 164 define a gap 174 thatfacilitates preventing contact between rotor 168 and housing 164 duringoperation of encoder 152.

Encoder 152 also includes a plurality of permanent magnets 176 that areoriented generally radially within rotor 168 such that a radiallyoutermost portion of each magnet 176 is substantially flush with rotorsurface 170. During rotation of rotor 168, magnets 176 generate amagnetic flux with a predetermined magnetic strength and orientation. Inthe exemplary embodiment, five magnets 176 are positioned substantiallycircumferentially equidistant from each other. Alternatively, any numberof magnets 176 with any circumferential separation that enables encoder152 to function as described herein may be used. One magnetic cycle isdefined as the rotational travel of rotor 168 from a first magnet 176 toa circumferentially adjacent next magnet 176.

Encoder 152 further includes two magnetic reed switches 178 and 179 thatare securely coupled to a switch holder 180 secured to housing 164. Inthe exemplary embodiment, switches 178 and 179 are approximately 18°apart to facilitate operation of encoder 152. Alternatively, switches178 and 179 may be positioned with any degree of circumferentialseparation that enables encoder 152 to function as described herein.Switches 178 and 179 each have a predetermined sensitivity selected tosubstantially cooperate with the magnetic flux of magnets 176. In theexemplary embodiment, switches 178 and 179 are circumferentiallyseparated at a distance that is approximately equivalent to one-quarterof a magnetic cycle and at least partially defines the relationshipbetween a first magnetic pulse and a second magnetic pulse as magnets176 rotate past switches 178 and 179. Moreover, in the exemplaryembodiment, five magnets 176 and two switches 178 and 179 facilitateattaining a predetermined resolution of travel of drill pipe 124. A pairof common power supply conduits 182 and 184 are electrically coupledwith switches 178 and 179, respectively. Conduits 182 and 184 areelectrically coupled with a power supply (not shown in FIGS. 2 and 3)positioned within interface device 154 (shown in FIG. 1). Moreover, acommon ground conduit 183 is electrically coupled with switches 178 and179 on the ends of switches 178 and 179 that are opposite to theconnections of conduits 182 and 184. Conduits 182, 183 and 184 areenclosed within encoder cable 156. In the exemplary embodiment, conduits182, 183 and 184 are copper wire. Alternatively, conduits 182, 183 and184 may be any electrically conductive devices that enable system 150 tofunction as described herein. Conduit 183, switch 178, and conduit 182at least partially define a first encoder channel 186 and conduit 183,switch 179 and conduit 184 at least partially define a second encoderchannel 188.

Encoder 152 facilitates reliability of system 150, and hence, drillingrig 100, due to the relatively small number of moving parts of system150 exposed to field conditions are mitigated and are fully containedwithin encoder 152. Specifically, only rotor 168 and switches 178 and179 utilize operational movement to affect the performance of encoder152 as described herein. In the event of malfunction, encoder 152 may beeasily and quickly replaced while mitigating disruption of drillingoperations. Moreover, encoder 152 may be sized such that redundantencoders 152 may be coupled to shaft 112 and/or replacement encoders 152storage requirements are mitigated.

During operation, drawworks drum 110 (shown in FIG. 1) retrieves orextends cable 114 (shown in FIG. 1) as a function of drill pipe depthwithin well 128 (shown in FIG. 1). As drum 110 is rotated by drawworksdrive shaft 112, encoder rotor 168 is rotated in the same direction. Forexample, as rotor 168 is rotated in the clockwise direction (asillustrated by the arrow) a magnet 176 successively approaches, rotatesby, and recedes from switch 178. Magnet 176 generates a magnetic fluxwith a predetermined magnetic strength and orientation such that as eachmagnet 176 approaches switch 178, at a predetermined circumferentialdistance away from switch 178, during the approach, switch 178 closes.Upon closing, switch 178 completes an electric circuit within firstchannel 186 such that an electric signal may be channeled from device154 via conduit 182 through switch 178 and back to device 154 viaconduit 183. Switch 178 remains closed until magnet 176 has receded apredetermined circumferential distance from switch 178. Magnets 176,device 154, and the components of second channel 188 including switch179, conduit 183 and conduit 184 operate together in a similar manner.The action of each of magnets 176 closing switch 178 defines a firstnegative magnetic pulse edge and the action of each magnet 176 closingswitch 179 defines a second negative magnetic pulse edge. This actionand subsequent actions associated with interaction of each magnet 176and switches 178 and 179 are discussed further below.

FIG. 4 is an electrical schematic of exemplary drill pipe positionmeasurement system 150 that may be used with drilling rig 100 (shown inFIG. 1). System 150 includes at least one encoder 152 that iselectrically coupled to interface device 154 via encoder cable 156.Interface device 154 is electrically coupled to data processing assembly158 that is coupled to an operator interface terminal (OIT) 160 via aplurality of electronic cables 162. Encoder 152 includes two magneticreed switches 178 and 179. Common power supply conduits 182 and 184 areelectrically coupled with switches 178 and 179, respectively. Moreover,common ground conduit 183 is electrically coupled with switches 178 and179 on the ends of switches 178 and 179 that are opposite to theconnections of conduits 182 and 184. Conduits 182, 183 and 184 areenclosed within encoder cable 156.

Conduit 183, switch 178, and conduit 182 at least partially define firstencoder channel 186. Channel 186 further includes a 5 volt directcurrent (VDC) power supply 190. Channel 186 also includes a 25,000 ohmcurrent-limiting resistor 191 electrically coupled to power supply 190and a power supply signal conduit 192 electrically coupled to conduit182 downstream of resistor 191. Channel 186 further includes a processor193 electrically coupled to conduit 192. Channel 186 also includes anelectrical grounding device 194 electrically coupled to conduit 183,power supply 190 and a ground conduit 195 electrically coupled toprocessor 193. Conduit 195 is also electrically coupled to conduit 183upstream of grounding device 194. Resistor 191, conduit 192, processor193, grounding device 194 and ground conduit 195 are positioned withininterface device 154. Therefore, first channel 186 is defined by powersupply 190, resistor 191, conduit 182, conduit 192, switch 178, conduit183, grounding device 194, conduit 195 and processor 193. Processor 193is coupled in electronic data communication with assembly 158 viaconduit 162.

Similarly, conduit 183, switch 179, and conduit 184 at least partiallydefine second encoder channel 188. Channel 188 further includes powersupply 190, a 25,000 ohm current-limiting resistor 196 electricallycoupled to power supply 190 and a power supply signal conduit 197electrically coupled to conduit 184 downstream of resistor 196. Channel188 also includes processor 193 electrically coupled to conduit 197.Channel 188 further includes electrical grounding device 194 and groundconduit 195. Resistor 196 and conduit 197 are positioned withininterface device 154. Therefore, second channel 188 is defined by powersupply 190, resistor 196, conduit 184, conduit 197, switch 179, conduit183, grounding device 194, conduit 195 and processor 193.

FIG. 5 is an exemplary graphical representation 200 of a plurality ofwaveforms that may be produced using encoder 152 (shown in FIGS. 2 and3) and system 150 (shown in FIG. 4). Ordinate 202 (Y-axis) represents anamplitude of an output signal voltage from switches 178 and 179 (bothshown in FIGS. 2 and 4) in voltage units. Abscissa 204 (X-axis)represents time units. Switch 178 facilitates channeling a first channeloutput signal 206 via first channel 186 (shown in FIGS. 2 and 4) andswitch 179 facilitates channeling a second channel output signal 208 viasecond channel 188 (shown in FIGS. 2 and 4). Signals 206 and 208 aresubstantially square-waved signals and are illustrated as slightlyoffset from each other in amplitude for clarity.

Signals channeled within first channel 186 are received by processor 193via conduits 192 and 195 and together form a first channel signal 206.An approximately five VDC voltage differential is applied to switch 178via power supply 190, resistor 191, conduits 183 and 182, and groundingdevice 194 (all shown in FIG. 4). Grounding device 194 facilitatessubstantially all signals channeled through conduit 195 to have avoltage amplitude of approximately zero VDC throughout operation ofsystem 150. When switch 178 is in an open condition electric currentflow through first channel 186 is substantially zero. Moreover, a signalthat has a voltage amplitude of approximately five VDC is channeledthrough conduit 192. Signal 206 includes a first channel “switch 178open” output portion 220 that represents a period of time switch 178 isopen, as well as an associated value of a voltage differential betweenconduits 192 and 195. Portion 220 graphically represents this voltagedifferential.

Similarly, signals channeled within second channel 188 are received byprocessor 193 via conduits 197 and 195 and together form a secondchannel signal 208. An approximately five VDC voltage differential isapplied to switch 179 via power supply 190, resistor 196, conduits 183and 184, and grounding device 194 (all shown in FIG. 4). Groundingdevice 194 facilitates substantially all signals channeled throughconduit 195 to have a voltage amplitude of approximately zero VDCthroughout operation of system 150. When switch 179 is in an opencondition electric current flow through second channel 188 issubstantially zero. Moreover, a signal that has a voltage amplitude ofapproximately five VDC is channeled through conduit 197. Signal 208includes a second channel “switch 179 open” output portion 222 thatrepresents a period of time switch 179 is open, as well as an associatedvalue of a voltage differential between conduits 197 and 195. Portion222 graphically represents this voltage differential. In the exemplaryembodiment, portions 220 and 222 of signals 206 and 208, respectively,are substantially similar.

Signal 206 also includes a first negative magnetic pulse edge 210 and afirst positive magnetic pulse edge 212. Edge 210 is generated as eachmagnet's magnetic flux exceeds a sensitivity threshold of switch 178 asmagnets 176 approach switch 178 and close switch 178. Edge 212 isgenerated as the magnetic flux in the vicinity of switch 178 weakens aseach magnet 176 recedes away from switch 178 and switch 178 is opened. A“switch 178 closed” portion 211 of signal 206 is defined and extendsbetween edges 210 and 212. Portion 211 is equivalent to the duration oftime that the strength of the magnetic flux in the proximity of switch178 exceeds the sensitivity threshold of switch 178 and an associatedvoltage differential across switch 178. When switch 178 is closed, anelectric current is permitted to be channeled through first channel 186,including switch 178, from power supply 190 to grounding device 194thereby decreasing the voltage amplitude of the signal channeled throughconduit 192 to substantially zero. Therefore, the voltage differentialbetween conduits 192 and 195 is substantially zero.

Similarly, output signal 208 also includes a second negative magneticpulse edge 214 and a second positive magnetic pulse edge 216. Also,similarly, a “switch 179 closed” portion 215 of signal 208 is definedand extends between edges 214 and 216. When switch 179 is closed, anelectric current is permitted to be channeled through second channel188, including switch 179, from power supply 190 to grounding device 194thereby decreasing the voltage amplitude of the signal channeled throughconduit 197 to substantially zero. Therefore, the voltage differentialbetween conduits 197 and 195 is substantially zero. In the exemplaryembodiment, portions 211 and 215 of signals 206 and 208, respectively,are substantially similar.

One magnetic cycle is defined as the rotational travel of rotor 168 froma first magnet 176 to a next magnet 176. One magnetic cycle is definedin FIG. 4 as 360°, i.e., 360° is substantially equivalent to the timeduration between edge 210 and the next generation event of edge 210.Subsequently, 90° is substantially equivalent to the time durationbetween edge 210 and edge 214. Also, 90° is equivalent to the timeduration between edge 214 and edge 212, and the time duration betweenedge 212 and edge 216. Moreover, 90° is substantially equivalent to thetime duration between edge 216 and the next generation event of edge210. This sequence of events is substantially replicated for eachmagnetic cycle. In the exemplary embodiment, encoder 152 includes fivemagnets 176 and each 360° rotation of encoder rotor 168 (shown in FIGS.2 and 3) generates five magnetic cycles. Therefore, each magnetic cycleis substantially equivalent to 72° of rotation of rotor 168 and eachquadrant of the 360° magnetic cycle, i.e., 90° of the magnetic cycle issubstantially equivalent to 18° of rotation of rotor 168.

Signal 206 leads output signal 208 as encoder 152 rotates in a clockwisedirection. In contrast, signal 208 leading output signal 206 indicatesencoder 152 is rotating in a counter-clockwise rotation. In theexemplary embodiment, the amplitude of voltage output signals 206 and208 during portions 220 and 222, respectively, is approximately fivevolts DC and substantially zero amperes current is channeled throughswitches 178 and 179. In contrast, the amplitude of voltage outputsignals 206 and 208 from switches 178 and 179, respectively, duringportions 211 and 215 is approximately zero volts DC. Moreover, duringperiods when portions 211 and 215 overlap, less than one-third of onemicrowatt of power is dissipated by system 150.

The exemplary magnitudes of voltage, current and power associated withsystem 150, including encoder 152, as described herein facilitatereducing potential for inadvertent electrical arcing associated withencoder 152 having sufficient energies to induce ignition ofpredetermined materials and compounds. Moreover, in the exemplaryembodiment, encoder 152 is not electrically coupled to any significantexternal power sources, i.e., power sources that are configured totransmit more than one microwatt of power. As such, encoder 152 may beused in applications wherein an intrinsically safe device is required,such as, but not limited to, Class I, Division 1 conditions. Suchconditions may exist within facilities that include, but are not limitedto, chemical plants, grain elevators, and natural gas transfer stations.Alternatively, any values of voltage, average power, peak power, averagecurrent and peak current that facilitates operation of encoder 152 asdescribed herein may be used.

Referring again to FIG. 1, during operation of rig 100 as cable 114 isextended from and refracted towards drum 110 to vary a depth of drillpipe 124, encoder 152, that is rotatably coupled to drawworks shaft 112,facilitates channeling output signals 206 and 208 that are transmittedto interface device 154 via conduits 182 and 184, respectively. Encoder152 is an incremental encoder 152 in that it measures relative depthfrom a starting depth and measures depth changes upward or downward fromthat starting depth. A preliminary set of data that corresponds to aninitial starting depth is manually input into system 150. Device 154 anddata processing assembly 158 receive a first set of signals 206 and 208and assembly 158 uses at least one resident conversion algorithm todetermine a first distance of drill pipe 124. As shaft 112 rotates tochange the depth of drill pipe 124 to a second position, a second set ofsignals 206 and 208 are channeled to device 154 that uses at least oneresident conversion algorithm to determine the number and polarity ofmagnetic cycles. The number and polarity of magnetic cycles asdetermined by device 154 is transmitted to data processing assembly 158wherein a plurality of conversion algorithms are executed to determine adistance of movement of drill pipe 124, a direction of movement, and arate of movement. Examples of conversion algorithms may include, but arenot limited to, integration algorithms to convert the number andpolarity of magnetic cycles that are representative of the distance anddirection of movement of drill pipe 124, to values that may beinterpreted by an operator. The processed signals are subsequentlytransmitted to OIT 160.

The methods and apparatus for monitoring a rotary machine shaft asdescribed herein facilitate operation and monitoring of a rotarydrilling rig. More specifically, the rotary encoder described hereinfacilitates an efficient and effective drill pipe depth measurementscheme. Also, the rotary encoder facilitates operation of a passiveoperating system with self-contained low-power components and noexternal power requirements, and is intrinsically safe in hazardousenvironments. Further, the rotary encoder also facilitates enhancingdrilling rig reliability, and reducing maintenance costs and drillingrig outages. Moreover, the rotary encoder also facilitates operation offacilities that include, but are not limited to, chemical plants, grainelevators, and natural gas transfer stations.

Exemplary embodiments of rotary encoders as associated with drill pipedepth measurement schemes are described above in detail. The methods,apparatus and systems are not limited to the specific embodimentsdescribed herein nor to the specific illustrated drilling rig.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method of determining the amount of travel of a rotating componentincluding a rotor shaft, said method comprising: providing aself-contained magnetically-powered encoder that includes at least oneencoder rotor that extends outward from a sealed housing such that aclearance gap is defined between the rotor and housing; rotatablycoupling the encoder to the rotor shaft; measuring a first position ofthe encoder rotor; determining a first rotational position measurementof the rotor shaft based on the encoder rotor; rotating the rotor shaftto a second rotational position; determining a direction of rotation anda second rotational position measurement of the rotor shaft using theencoder; and determining a total rotational distance traveled by therotor shaft between the first and second rotational positions.
 2. Amethod in accordance with claim 1 wherein providing an encoder furthercomprises: providing an encoder including a plurality of magnets coupledwithin at least a portion of the rotor; and coupling a plurality ofswitches to at least a portion of the housing, wherein the plurality ofswitches are oriented to receive magnetic flux generated from theplurality of magnets.
 3. A method in accordance with claim 1 whereinrotatably coupling the encoder to the rotor shaft comprises: providing adrawworks including a least one cable drum rotatably coupled to a driveshaft; and rotatably coupling the encoder to the drawworks drive shaft.4. A method in accordance with claim 3 wherein measuring a firstposition of the encoder rotor comprises coupling a drilling tool to atleast one cable that is coupled to the drawworks cable drum.
 5. A methodin accordance with claim 1 wherein determining a first rotationalposition comprises transmitting the encoder first position measurementto a remote processor that is programmed with at least one conversionalgorithm.
 6. A method in accordance with claim 1 wherein rotating therotor shaft to a second position comprises re-positioning a drillingtool by rotating a cable drum and the at least one encoder rotorsubstantially simultaneously.
 7. A method in accordance with claim 1wherein determining a direction of rotation and a second rotationalposition measurement of the rotor shaft comprises rotating at least oneencoder magnet having a magnetic flux past at least one encoder switch,wherein the magnetic flux generated causes one of opening and closingthe at least one switch.
 8. A method in accordance with claim 1 whereindetermining a direction of rotation and a second rotational positionmeasurement of the rotor shaft comprises: rotating at least one encodermagnet having a magnetic flux past a plurality of encoder switches thatare spaced circumferentially across a surface of the encoder housing,wherein the magnetic flux generated causes one of opening and closing ofat least one encoder switch; generating a plurality of output signalsbased on the movement of each encoder switch; and transmitting theplurality of encoder output signals to a remote processor that includesat least one of a direction of rotation algorithm, and at least oneconversion algorithm.